1. Field of the Invention
This invention relates to a method for a treatment of sewage or waste water to re-use as a water and to an apparatus for the method. More particularly, the invention relates to a method for a treatment of sewage to remove suspended matter, organic matter, foaming matter and so on contained in the sewage, and also to an apparatus for the method.
2. Description of the Prior Art
In recent years, ration of the supply of the city water as well as restriction of the sewage have been tightened and re-use of the water has become all the more necessary especially in urban communities. Under such circumstances, a concentrated purification installation and a water re-use recycling system have been used in newly constructed buildings in cities or in housing developments partly because of absence of sufficient sewage system capable of processing great quantities of sewage. Such recyling systems are referred to as a "re-use system" or as a "water re-use processing system" in contast with the conventional water supply and sewage systems.
Applications of the reused water are versatile and varied. At present, however, the reused water is used in the fields such as flush water for flush toilets, water for air-conditioning, water for car cleaning and water for leisure applications.
As a general standard for the water quality, it has been believed necessary that the reused water should contain, in the case of the flush water for the flush toilets, up to 10 ppm of suspended matter, up to 20 ppm of organic matter, up to 5 ppm of foaming matter, up to 20 ppm of nitrogen compounds and desirably the number of Escherichia coli of up to 1,000/ml. When the reused water is used for air-conditioning, car cleaning or leisure purposes, it is believed necessary as the water quality standard that the water should contain up to 5 ppm of suspended matter, up to 10 ppm of organic matter, up to 1 ppm of foaming matter, up to 10 ppm of nitrogen compounds and the number of Escherichia coli of up to 1,000/ml.
The water re-use processing systems that have so far been proposed to satisfy the abovementioned water quality standards consist principally of a biochemical processing or a physicochemical processing. The former comprises, as a principal method, an active sludge method and a spray filtration bed method used in the conventional sewage processing in combination with a foam sedimentation-separation method and (or) a sand filtration method. However, this processing system involves the drawback in that the installation space is large and the processing speed is slow.
For the abovementioned reason, the latter using the physicochemical processing method has been attempted.
As disclosed in Japanese Patent Laid-Open No. 89676/1974, removing first suspended matter by electrolytic floating and separation, carrying out then again the floating separation to remove the rest of suspended matter and thereafter decomposing organic matter having COD or BOD by means of the electrolytic oxidation. Though this method uses two water processing methods, i.e., the floating-separation method and the electrolytic oxidation method, the method has not yet come to provide sufficient effects as a water re-use system and to satisfy the aforementioned water quality standards.